Neutral metalloendopeptidase 3.4.24.11 (Neprilysin, NEP) is a protease located on the surface of a wide variety of cells in the nervous system in a localization which suggests a modulatory role in the metabolism of endogenous opiate compounds. Within the lung, the enzyme may suppress neurogenic inflammation induced by tachykinins and potentially regulates endogenous growth factors such as bombesin-like peptides. Renal expression of NEP appears to abrogate the activities of a variety of cardiovascular regulatory peptides such as atrial naturetic factor and endothelin. In the immune system, the enzyme is expressed on pro B cells and neutrophils, where it was characterized as the common acute lymphoblastic leukemia antigen, CALLA. The objective of this research program is to explore the central hypothesis that NEP serves as a biological control mechanism to modulate the actions of diverse biologically active peptides in the brain, lung and immune system. Secondary hypotheses are that alternative processing of the NEP gene leads to a biologically novel enzyme MME II and that the enzyme itself is subject to regulation . Five specific aims are proposed to test these hypotheses. Aims 1-3 will characterize the phenotype of mice engineered genetically deficient in NEP expression. We will focus on three well characterized models (analgesia/enkephalinase; tachykinin-induced inflammation and bronchoconstriction/NEP; and ontogeny of the lymphoid compartment/CALLA) where inhibitor studies have suggested a possible key role for the enzyme as a biological modulator. Aim 4 will construct and characterize a cDNA for MME Il, measure the tissue distribution of the transcript quantitatively, and characterize the protein in vitro and potentially in vivo. Aim 5 examines the possibility for protein downregulation through phosphorylation/internalization. The successful completion of these aims should clarify the role of the enzyme as a critical modulator of diverse processes mediated by neuropeptides and other biologically active peptides, and provide new insights into how the organism has adapted this protease to biological control. The potential for therapeutic intervention at the NEP system in opiate/alcohol dependance, pain control, heart failure and neurogenic inflammation of the lung will be advanced by these studies.